Image caption Zac Goldsmith quit as a Conservative, in opposition to policy on Heathrow Airport

The polls have closed in the Richmond Park by-election, triggered by the Conservative MP”s resignation over government policy on Heathrow Airport.

Zac Goldsmith hopes to be re-elected as an independent, having quit when the government decided to back a third runway at the west London airport.

But the Lib Dems have sought to make his pro-Brexit stance an issue in a seat with many pro-EU voters.

The Conservatives had a majority of 23,015 at the 2015 general election.

Mr Goldsmith, first elected in 2010, held his seat at the 2015 general election, with an increased majority and 58.2% of the vote.

The Lib Dems came second with 19.3% of the vote – having seen a big drop in support since 2010, in common with Lib Dem performance across the country, following five years in coalition.

Flight path

Mr Goldsmith quit in October after the government announced it would back a third runway at Heathrow to expand UK airport capacity.

The long-standing environmental activist, who failed in his bid to become mayor of London earlier this year, had pledged during both the 2015 and 2010 general election campaigns to resign if the government backed plans to build a new runway at Heathrow, the UK”s busiest airport.

Image caption Sarah Olney (left) had some celebrity support on the campaign trail

The Richmond Park seat, one of the wealthiest constituencies in the country, which was held by the Lib Dems prior to 2010, is one of many in south-west and west London beneath Heathrow”s flight path.

Mr Goldsmith has described himself as “the best bet we have of stopping expansion” and told the Guardian: “I believe we will win this battle.

“In addition to the noise, cost, air pollution and appalling congestion implications, the sheer complexity involved in building the third runway means that with the right campaign, it is unlikely ever to happen.

“I will do all I can to make sure of it.”

But the constituency, which takes in parts of the south-west London boroughs of Richmond and Kingston-upon-Thames, also voted heavily to remain in the European Union, and the Lib Dems, who also oppose Heathrow expansion, have been making Brexit the dividing issue in the by-election campaign – Mr Goldsmith was among senior Conservatives to come out in favour of leaving the European Union.

Lib Dem candidate Ms Olney had some celebrity support from rock star Sir Bob Geldof this week, thanks to her anti-Brexit stance.

She told the Guardian that her party was hoping to pull off a huge by-election upset on the back of support from Remain voters.

“Liberal Democrats have a history of famous by-election triumphs, but this would be the most important yet.

“Our victory at Ribble Valley killed off the poll tax.

“A victory for the Liberal Democrats here could kill off hard Brexit.”

The Conservatives, UKIP and the Green Party are not fielding candidates.

The Tories and UKIP are backing Mr Goldsmith, while the Greens” Caroline Lucas says Lib Dem Sarah Olney is “the best hope” of beating Zac Goldsmith and “denting the government”s plans for a painful Brexit”.

Writer and railway historian Christian Wolmar is standing for Labour – despite calls from some frontbenchers for the party to stand aside to give the Lib Dems a better chance of winning the seat.

Mr Wolmar says his campaign shows there are “no no-go areas for Labour”, adding that while Mr Goldsmith wanted the by-election to be “a referendum on Heathrow… the key issue for local people is clearly Brexit”.